Attempting to retrieve the build dependencies for sawfish fails:

% aptitude build-dep sawfish
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reading extended state information
Initializing package states... Done
Reading task descriptions... Done
Unable to satisfy the build-depends: Build-Dependsautomake1.10.Unable to satisfy the build-depends: Build-Dependsautomake1.10.No packages will be installed, upgraded, or removed.
0 packages upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0B of archives. After unpacking 0B will be used.
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reading extended state information
Initializing package states... Done
Reading task descriptions... Done

The same task with apt-get:

% apt-get build-dep sawfish
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

automake1.10 (referenced by the aptitude run) is installed:

% dpkg -l automake
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name           Version        Description
+++-==============-==============-============================================
ii  automake       1:1.10.1-3     A tool for generating GNU Standards-complian

package aptitude
merge 509100 512034
quit

Hi Diab,

I'm merging your bug with
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=509100

Regards,
Steve

I found a workaround. If you need to install build dependencies for
package X, just create a fake package, which has "Depends", which are
equal to X's "Build-Depends". Then install this fake package via
aptitude.

Possibility of such workaround means that aptitude already has all
needed machinery. We just need to make aptitude to treat
"Build-Depends" in similar way to "Depends"